This invention is related generally to phosphors for plasma display panels. More particularly, this invention is related to green-emitting borate phosphors.
In order to achieve full color reproduction, a plasma display panel (PDP) is composed of pixels which emit light corresponding to the three primary colors of red, green and blue. The pixels are formed from red-, green-, and blue-emitting phosphors which have been deposited in a paste or ink form on an inner wall of the device. The binder materials are then burned out at a high temperature (about 400xc2x0 C.). The tri-color emission is achieved by stimulating the phosphors with vacuum ultraviolet (VUV) radiation generated by Xe-Ne gas discharges (172 nm). The luminous efficiency, color chromaticity, afterglow, and stability of the phosphors have significant roles in the PDP performance. Typical phosphors used in PDP applications include a red-emitting (Y,Gd)BO3:Eu phosphor (YOB), a green-emitting Zn2SiO4:Mn phosphor, and a blue-emitting BaMgAl10O17:Eu.
The conventional green-emitting Zn2SiO4:Mn phosphor suffers from a long decay time and a decreasing luminous efficiency which negatively affects panel characteristics. A potentially more effective green-emitting phosphor is yttrium gadolinium terbium borate, (Y,Gd,Tb)BO3. The luminescence properties of a Y0.95-xGdxTb0.05BO3 phosphor system in the VUV region have been described by Kwon et al. J. Luminescence 87-89 (2000) 1039-1041. Japanese Patent Application 11-071581 to Ohto describes a green-emitting (Y,Gd,Tb)BO3 for use in plasma display panels. The (Y,Gd,Tb)BO3 phosphor exhibits a higher VUV absorption at 172 nm and experiences a smaller decrease in brightness after binder burnout.
It has been discovered that substituting a small amount of lanthanum for yttrium improves the brightness of the (Y,Gd,Tb)BO3 phosphor under VUV excitation. The substituted phosphor has the general formula:
(Y(1-x-y-z)GdxTbyLaz)BO3
where
0.01xe2x89xa6xxe2x89xa60.4,
0.01xe2x89xa6yxe2x89xa60.1, and
0 less than zxe2x89xa60.2.
Preferably, 0.2xe2x89xa6xxe2x89xa60.3, 0.03xe2x89xa6yxe2x89xa60.07 and 0.05xe2x89xa6zxe2x89xa60.15. More preferably, 0.05xe2x89xa6zxe2x89xa60.1. The phosphor exhibits a bright green emission (CIE color coordinates; x=0.323, y=0.610) under VUV excitation. However, increasing the amount of lanthanum above the specified range causes a decrease in the VUV brightness.